In recent years, the use of a long-distance large-capacity optical communication network has spread and the development of high-speed large-capacity WDM (Wavelength Division Multiplex) transmission systems has progressed.
In addition, attention is paid to SOAs (Semiconductor Optical Amplifiers) which change the gain according to driving current as optical amplifiers in optical communication networks.
An SOA is an optical amplifier including an optical amplification element made from a compound semiconductor such as indium phosphorus (InP). Compared with EDFAs (Erbium Doped Fiber Amplifiers) using an erbium (Er) doped fiber as an amplification medium, SOAs are, for example, small and have wide amplification bands. SOAs have these advantages, so they have come to be widely applied to optical communication networks.
The following techniques regarding optical amplification control by an SOA were proposed as prior arts.
Japanese Laid-open Patent Publication No. 2009-200633
Japanese Laid-open Patent Publication No. 2010-186919
In order to reduce a time delay in the flowing of driving current to an SOA chip after the generation of applied voltage, an edge enhancement is performed on the applied voltage at the time of optical amplification by an SOA. However, there may be a change in the power of a light inputted to the SOA. In this case, performing an edge enhancement the size of which is fixed on applied voltage without taking the change into consideration causes distortion of the waveform of an amplified light outputted from the SOA.